If Norwegian prosecutors get their way, no one will be held criminally responsible for the deaths of 77 people in a bomb and shooting rampage that shook the peaceful nation.

Even though self-styled anti-Muslim militant Anders Behring Breivik insists he is sane and that he carried out the July 22 attacks for political reasons, prosecutors said in closing arguments Thursday that doubts about his mental state mean he should be sent to a psychiatric institution instead of prison.

Ultimately, it's up to the Oslo district court to decide whether Breivik is criminally insane when it presents its ruling, expected a month after the trial ends on Friday (local time).

Either way, the 33-year-old Norwegian will likely be locked up for most, if not all, of his life. But the outcome will also influence whether Norway's worst peacetime massacre goes down in history as right-wing terrorism or as the work of a bloodthirsty madman.

"I still think Breivik is clearly sane and that his rhetoric, attitudes and behaviour don't differ notably from other terrorists," said Usman Rana, a Muslim immigrant and newspaper columnist in Norway.

Rana said he doubted the psychiatric dimension would have been so prominent if the perpetrator had been an Islamist extremist.

The image of global terrorism was jolted when the blond, blue-eyed gunman surrendered to police after slaughtering 69 people at the governing Labor Party's summer youth camp. Hours earlier, he had set off a bomb in Oslo's governing district, killing eight.

Breivik immediately admitted to the attacks and called them justified. The left-wing Labour Party, in power for much of the postwar era, had betrayed the country by allowing Muslim immigrants to settle in Norway, he said.

That kind of rhetoric is not uncommon among far-right fanatics in Europe, but Breivik didn't belong to any known extremist group.

He claimed to be a commander of a militant network of ``Knights Templar``, but investigators found no trace of it.

Even when presented with evidence to the contrary, Breivik insisted the group is real with such conviction that he must actually have believed in it, prosecutor Svein Holden said.

"On the background of Breivik's intense defence of these obviously false claims, we believe it's hard to conclude that it's an intentional lie on his part," Holden said.

The defence is likely to refute the insanity finding on Friday, the last day of the 10-week trial. Before leaving the court room Thursday, Breivik defiantly flashed a clenched-fist salute for the first time since the first week of the trial.

Many Norwegians are not so sure that he is delusional.

A poll by research firm Norstat released on Thursday by Norwegian public broadcaster NRK showed 74 percent of Norwegians believe Breivik was mentally competent to be sentenced to prison. Ten percent said he was criminally insane, while the rest were undecided in the June 12-19 survey of 1,000 people. The margin of error was about 3 percentage points.

Prosecutors said their decision was based on Norwegian rules stating that defendants cannot be sentenced to prison if there is reasonable doubt about their mental health.

"When the court interprets the current rules, what people think cannot be of any relevance," Prosecutor Inga Bejer Engh said after the hearing on Thursday. "When this case has been legally decided, we can sit down and have a discussion: Are the rules we have out of phase with the people?"

She also said people shouldn't worry about Breivik getting out any sooner if he's sent to a mental institution rather than a prison.

"We have murderers who have been sentenced to psychiatric care who will probably never get out again," Engh said, noting that none of them had killed 77 people.

The first team diagnosed him with "paranoid schizophrenia," a serious mental illness which would preclude a prison sentence. The second team found him legally sane, saying he suffers from a dissocial and narcissistic personality disorder, but is not psychotic.

If the court opts for a prison term instead, prosecutors said their preference would be the maximum sentence of 21 years. A sentence can be extended beyond that if a prisoner is considered a menace to society.

Some of those who lost family members in the massacre were disappointed by the prosecution's decision.

"They think that imprisonment would be a more justified outcome of what happened on July 22," said Mette Yvonne Larsen, a lawyer for the bereaved.

Others said that whether Breivik spends the rest of his life in prison or in a mental institution is not the most important issue.

"I've lost the dearest thing I had," said Trond Henry Blattmann, whose 17-year-old son was killed in the shooting massacre on Utoya island. "It doesn't matter whether it's prison or hospital."